The problem of minimizing the level of background light which will limit the sensitivity of any photometric measurements has commonly been dealt with in the prior art by using optical cement to join optical elements permanently or by using an optical grease of a near-matching index of refraction. However, these expedients are somewhat awkward, tend to be messy, dirt-catching and are difficult to control.
Where it is desired to measure some property of a liquid or a particle suspended in a liquid which is contained in a tube or cuvette of cylindrical side wall or spherically curved bottom, these curved surfaces can be neutralized by immersion of the tube in a fluid of matching refractive index. Here again, the awkwardness of working with optical fluids is encountered, along with their tendency to become contaminated and the requirement for cleaning and replacement.
The objective of the invention, therefore, is to deal with reflected, refracted and scattered background light in optical measuring systems in a wholly different manner which does not require the use of optical cements or optical greases or fluid immersion of specimen containers and the like. In accordance with the invention, the level of background light is minimized through the use of a conformable optical coupler between opposing rigid optical elements, whether in the form of specimen containers, light detectors, light pipes or lenses. More particularly, a compliant or conformable coupling member with a refractive index in the range of 1.45 to 1.55 is interposed between spaced opposing optical elements, and through the application of forces to the coupling member and/or to the opposing optical elements, the compliant coupler is forced into intimate contact with the surfaces of the optical elements and conforms to the configurations of their surfaces. The material forming the conformable optical coupler, such as silicone rubber, is stable, transmits at least the visible spectrum, is readily castable and washable. Other suitable conformable materials may be employed.
The use of the conformable optical coupler in accordance with the invention substantially eliminates the above-noted problems of the prior art.
Other objects and advantages of the invention will become apparent during the course of the following detailed description.